Burner for dental furnaces.



05H LAND. BURNER FOR DENTAL FURNACES.

APPLICATION FILED APR. 22. 1914.

Patented May 22, 1917.

2 SHEETS--$HEET 1.

W/T/VESSES A TTOR/VEYS c. H. LAND.

BURNER FOR DENTAL FURNACES.

APPLICATION FILED APR.22, 19H.

Patented May 22, 1917.

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UITE STAT ion.

BURNER non DENTAL summons.

Specification of Letters Patent.

Patented May 22, 1917.

Application filed April 22, 1914. Serial No. 833,672.

To all whom it may concern:

Be it known that I, CHARLES H. LAND, a citizen of the United States, anda resident of Detroit, in the county of Wayne and State of Michigan,have made certain new and useful Improvements in Burners for DentalFurnaces, of which the following is a specification.

My invention relates to improvements in furnaces, "particularly thosefurnaces which are used in dental, metallurgical, and other similaroperations requiring a high heat, and it consists in the combinations,constructions and arrangements herein described and claimed. v

An object of my invention is to provide a furnace in which extremelyhigh temperatures may be had by'the use of ordinary illuminating gas,producer gas, etc., which are ordinarily not considered capable of beingused successfully owing to the fact that it is extremely difficult toprevent the ignition of the charge in the mixing chamber, therebycausing an explosion.

Other objects and advantages will appear in the following specification,and the novel features of the device will be particularly pointed out inthe appended claims. I

My invention is illustrated in the accompanying drawings forming part ofthis application in which similar reference characters indicate likeparts in the several views and in which Figure 1 is a vertical sectionthrough the furnace,

Fig. 2 is a face view of a portion of the removable auxiliary airconduit, certain parts being shown in section,

Fig. 3 is a view of the under side of a modified form of the auxiliaryair conduit,

Fig. 4 is a section at right angles to Fig. 1 along the line 4-4 of Fig.1,

Fig. 5 is a plan view of the lower portion of the furnace, the topportion having been removed.

In carrying out my invention I provide a base portion 1 of highlyrefractory ma terial. In the drawings I have illustrated this baseportion as being of a substantially cylindrical shape, but it is obviousthat it might be of other shapes without departing from the spirit ofthe invention. Around the sides and bottom of the base'portion 1 is ametal casing 2, while legs 3 are secured to the bottom of the casing inthe manner integral extension 5 at. its lower end, the

upper end being secured to'the bottom of the casing 2 in any suitablemanner.

Communicating with the extension 5 is a pipe 6' which is provided with avalve 7.

This pipe is designed to 'supply'gaseous fuel,

while at the bottom of the extension 5 is a pipe 8 communicating with aflexible tube 9, this tube being designed to supply air to the gaseousfue 'As will be seen from Fig. 1 the base 1 is provided with a centralrecess 1. Disposed within the recess 'l"' is a' removable refractoryblock 10'whose lower end' rests on the inclined walls'of the mixingchamber 4 and whose upper end is disposed normally below theuppersurface ofthe base 1. This block forms oneof the main features of theinvention, although, aspointed out above, it does not form the onlyfeature. It consists preferably of a body portion of carborundum havinglongitudinal passages 11 extending therethrough,these passages beingpreferably disposed in parallel relation. As will be seen from,Figs.land 5 the passages are relatively small so as to provide a large numberof passages in a block of relatively small size. While the manner inwhich the block is perforated with these passages forms no part of thepresent invention, at the same time the dimensions of the block and ofthe passages as well as the fact that I have been able to make'the blockof carborundum, which is one of the most refractory materials known,does have a direct bearing on the successful operation of the device. f

The upper part of the furnace consists of a body portion 12 ofrefractory material hollowed out to provide a combustion'chamher. Thebody portion 12 is inclosed in, a metal casing 13 which is preferablyprovided at its bottom'with an annular flange 14 secured to the casingby screws or in any other suitablemanner, this flange 14 having ashoulder 14 arranged to rest against a shoulder 2* formed on the lowercasing 2,

the arrangement being such that a lap joint is provided, as shown. Thetop part of the body portion is reduced and is provided with a cap 15.

Communicating with the combustion chamber is a laterally extendingopening 16 which is arranged to receive a muflie 17 The latter issupported by cross members 18 of highly refractory material 'such ascarborundum. A frame 19 bearing a shelf 20 is secured to the outercasing 13. The pur pose of the shelf 20 is to temporarily supportmaterials to be heated. 'After the muffle is inserted the opening 16around the muflie is closed by means of lute 16*. The mouth of theopening is beveled as shown at 16 From the foregoing description of thevarious parts of the device the operation thereof may be readilyunderstood.

It will be noted that the extension 5 is provided with air inlets 21which may be covered by pivoted closures 22 to exclude the air when itis so desired. I have found that with certain gases, as for instanceilluminating gas, it is better to keep the closures 22 over the openings21 when the device is first started up and then to open them afterward.The gas passing through the pipe 6 into the mixing chamber 4: is mixedwith the air coming through the pipe 8 and forms an eflicient mixturefor obtaining perfect combustion. The mixture passes up through thepassages 11 and is" ignited, and the flames play upon the mume 17.

In order to produce the greatest heating effect and to render the deviceable to retain heat for a long time I fill the space above the mufliewith refractory particles or balls such as those shown at 23 in Fig. 4.I have found that these provide sufficient draft for the products ofcombustion, but they become highly heated and thus present a heatretaining member immediately adjacent to the muflle. The heat which maybe attained by this device is very great. It is suflicient to meltplatinum. The air coming through thetube 9 is preferably under pressure.

The perforations in the refractory block 10 break up the streams of gasand air in such a manner as to insure a thorough mixing of the latterand the most perfect combustion. The great trouble in furnaces of thiskind has been that the screens or gratings which have been used did notprevent the ignition of the charge in the mixing chamber, therebyresulting in an explosion which would render the device useless. Thehigh temperature attained in the combustion chamber would eventuallyraise the gases in the mixing chamber to the kindling temperature. Ihave succeeded in preventing the striking back or the explosion ofthecharge in the thereby causing an explosion.

factors among others which lead to the successful use of this furnace.

First: The block 10 being made of car borundum is absolutely refractoryfor any temperature at which this furnace is designed to work;

Second: The passages are small enough to prevent a flame from fallingback into the.

mixing chamber; and

Third: Although equally important, the block is of such a length thatthe refractory material which is a very poor conductor of heat cannotconduct enough heat from the top of the block to the bottom thereof toever raise the kindling temperature of the gases inside the mixingchamber to their ignition point, for it will be observed that the coolgases striking the bottom of the refractory block 10 tend to cool theblock whose upper end, of course, is subject to intense heat.

A perforated screen or grating of metal will not answer the. purpose ofthe refractory block, since no matter how long the metal grating may beevidently enough heat is conducted by the metal to raise the kindlingtemperature of the gases in the mixing chamber to their ignitiontemperature, Further more, a metal grating or block would fuse far belowthe temperature which is required for such operations as formingartificial teeth or for melting platinum. Moreover, a block ofrefractory material having small passages will not prevent explosions inthe mixing chamber if'the block is not of sufficient length so that itwill prevent the conduction of heat from the upper end which is adjacentto the combustion chamber to the lower end which is receiving the gases.I have tried refractory blocks of such thickness or length that theywould stand a high temperature and not fuse, but it was only afterconsiderable experiment that I was able to determine that a refractoryblock could be made of sufficientlength to absolutely prevent any suchexplosion.

Another feature to which I desire to call particular attention is themeans by which I prevent any disastrous effects from the cracking of themufiie or oven upon articles such as artificial teeth which are beingbaked therein. It is a. well known fact that the carbon monoxidconstituent of the gas is the agent which destroys the color in teeth ifthe muffle should crack and permit the gas to enter the interiorthereof. To prevent this I provide a conduit which consists preferablyof a slab 24 of refractory material such as carborundum having thereinpassages 25. This slab is placed on the floor of the mufl'le and apassage 25 is connected by means of a flexible tube 26 with a branchpipe 27 leading from the air pipe and providedwith a valve 28. Any ofthe passages 25 may be connected with the tube 26 so as to deliver theair at approximately the point desired.

In the ordinary operation of baking teeth the plastic matter which is toform the tooth is molded to the shape and is then placed on a refractorytray 29 in Fig. 1. The tooth to be baked is shown at 30. During thefiring operation air is admitted through the tube 26 and through thepassage 25 and passes to the rear end of the muffle where it emerges atan exceedingly high temperature. If by chance during the firingoperation the muffle should crack and admit carbon monoxid the oxygen ofthe highly heated air would immediately unite with the carbon monoxid toform carbon dioxid which is not injurious to the teeth being baked. Bythis expedient I overcome any danger of discoloration of the product,owing to the action of the carbon monoxid gas.

' It may be that at times it will be desirable to pass into the fuelpipe hydrocarbons of particular composition in order to accomplishparticular results. Thus in certain metallurgical operations it may beadvisable to introduce hydrocarbons or other suitable fuels through abranch pipe 32 leading directly into the pipe 6, as shown in Fig. 1.

In Fig. 3 I have shown a modified form of the slab 24. In this figurethe slab 24: is shown as having a recess 33 in its bottom which isarranged for the reception of the end of the pipe or other suitableconduit. Radially extending grooves 34 carry the gases to variousportions of the interior of the muffle. It will be understood that Fig.3 shows a bottom view of the slab so that when it is turned over thebottom of the muifie will form one of the walls of the conductingpassage.

Another feature to which I desire to call particular attention is thefact that varying temperatures may be secured by the use of the samekind of gas and the same air pressure by a proper distribution of theburners. I have found that a burner of given area will maintain atemperature of 3200 F. in a combustion chamber of certain size. This issuflicient to melt platinum. \Vith a combustion chamber of larger size atemperature of 2600 may be maintained, while with one of still largersize a temperature of 1800 may be had, and in each of these cases theburners is working at its maximum efli-- ciency. By constructing thefurnace in acrality of passages extending therethrough,

the length of the block being such that the temperature ofthe end of theblock adjacent the mixing chamber is never above the kindling point ofthe gases within the mixing chamber.

2. In a furnace, a combustion chamber, a mixing chamber, a highlyrefractory block disposed between said mixing chamber and saidcombustion chamber, said block being provided with a plurality ofpassages for establishing communication between the mixing chamber andthe combustion chamber, each of said passages being relatively small indiameter, and said block being comparatively long so as to preventconduction of heat from said combustion chamber to said mixing chamber,means for introducing gas into said mixing chamber, an air pipe forintroducing air into said mixing chamber, said air pipe being providedwith a lateral opening communicating with the atmosphere, and means forcovering said lateral opening at will. i

3. In a furnace, a mixing chamber, a combustion chamber, and means forconducting gaseous fuel from said mixing chamber into said combustionchamber and for preventing the ignition of the charge in the mixingchamber by heat from the combustion chamber, said means comprising ablock of carborundum having a plurality of passages extendingtherethrough of relatively small diameter, the length of the block beingsuch that the temperature of the end of the block adjacent to the mixingchamber is ,never above the kindling point of the gases within themixing chamber,

CHARLES H. LAND.

Witnesses:

R. A. STANLEY, SoLoN C. KEMoN.

Copies of this patent may be obtained for five cents each, by addressingthe Commissioner of Patents, Washington, D. (1.

